Frequency synthesizer and frequency synthesis method thereof

Abstract

A frequency synthesizer and a frequency synthesis method thereof are provided. The frequency synthesizer includes a phase-locked loop unit, a voltage-controlled oscillating unit, and a frequency mixing unit. The phase-locked loop unit receives a reference signal and a feedback injection signal and generates a first oscillating signal according to the reference signal and the feedback injection signal. The voltage-controlled oscillating unit receives the feedback injection signal and generates a second oscillating signal according to the feedback injection signal. The frequency mixing unit is coupled to the phase-locked loop unit and the voltage-controlled oscillating unit, receives the first oscillating signal and the second oscillating signal, and mixes the first oscillating signal and the second oscillating signal to generate the feedback injection signal and an output signal.

What is claimed is: 
     
       1. A frequency synthesizer, comprising:
 a phase-locked loop (PLL) unit, receiving a reference signal and a feedback injection signal, and generating a first oscillating signal according to the reference signal and the feedback injection signal; 
 a voltage-controlled oscillating unit, receiving the feedback injection signal, and generating a second oscillating signal according to the feedback injection signal; and 
 a frequency mixing unit, coupled to the phase-locked loop unit and the voltage-controlled oscillating unit, receiving the first oscillating signal and the second oscillating signal, and mixing the first oscillating signal and the second oscillating signal to generate the feedback injection signal and an output signal. 
 
     
     
       2. The frequency synthesizer according to  claim 1 , wherein the feedback injection signal is a differential frequency signal generated by the frequency mixing unit according to the first oscillating signal and the second oscillating signal. 
     
     
       3. The frequency synthesizer according to  claim 1 , wherein the phase-locked loop unit comprises:
 a frequency divider, coupled to the frequency mixing unit, receiving the feedback injection signal, and performing frequency-division to the feedback injection signal to generate a frequency-division signal; 
 a phase frequency detector, coupled to the frequency divider, receiving the reference signal and the frequency-division signal, and generating a phase difference signal according to the reference signal and the frequency-division signal; 
 a charge pump, coupled to the phase frequency detector, receiving the phase difference signal, and generating a charging signal according to the phase difference signal; 
 a loop filter, coupled to the charge pump, receiving the charging signal, and generating a control signal according to the charging signal; and 
 a first voltage-controlled oscillator, coupled to the loop filter, receiving the control signal, and generating the first oscillating signal according to the control signal. 
 
     
     
       4. The frequency synthesizer according to  claim 3 , wherein the frequency divider is an integer frequency divider. 
     
     
       5. The frequency synthesizer according to  claim 1 , wherein the voltage-controlled oscillating unit comprises:
 a frequency multiplier, coupled to the frequency mixing unit, receiving the feedback injection signal, and performing frequency-multiplication to the feedback injection signal to generate a frequency-multiplication signal; and 
 a second voltage-controlled oscillator, coupled to the frequency multiplier, receiving the frequency-multiplication signal, and generating the second oscillating signal according to the frequency-multiplication signal. 
 
     
     
       6. The frequency synthesizer according to  claim 5 , wherein the frequency multiplier is an integer frequency multiplier. 
     
     
       7. The frequency synthesizer according to  claim 1 , wherein the frequency mixing unit comprises:
 a frequency mixer, coupled to the phase-locked loop unit and the voltage-controlled oscillating unit, receiving the first oscillating signal and the second oscillating signal, and mixing the first oscillating signal and the second oscillating signal to generate a mixed-frequency signal and the output signal; and 
 a mixer filter, coupled to the frequency mixer, receiving the mixed-frequency signal, and generating the feedback injection signal according to the mixed-frequency signal. 
 
     
     
       8. The frequency synthesizer according to  claim 7 , wherein the frequency synthesizer further comprises:
 an output filter, coupled to the frequency mixer, receiving the output signal, and low-pass filtering or high-pass filtering the output signal. 
 
     
     
       9. A frequency synthesis method of a frequency synthesizer, comprising:
 providing a phase-locked loop unit, wherein the phase-locked loop unit generates a first oscillating signal according to a reference signal and a feedback injection signal; 
 providing a voltage-controlled oscillating unit, wherein the voltage-controlled oscillating unit generates a second oscillating signal according to the feedback injection signal; and 
 providing a frequency mixing unit, wherein the frequency mixing unit mixes the first oscillating signal and the second oscillating signal to generate an output signal and the feedback injection signal.